This is one Novarossi #7 short body "Ultra" Turbo glow plug. This is a cold glow
plug intended for use in .21 race engines with high nitro content fuels.

The "Ultra" line of plugs from Novarossi are different from regular
plugs in that the hole where the filament is located is slightly larger
in diameter, and the glow plug element has a special coating. The new
coating is intended to make the plug be more durable, while the larger
diameter hole is designed to improve the idle and throttle response of
the engine.

The Novarossi line of "Turbo"glow plugs are available in the following variations:

#5TC/TF - Hot glow filament plug

#6TC/TF - Medium filament glow plug

#7TC/TF - Cold filament glow plug

#8TC/TF - Very cold filament glow plug

The
difference between the TC (Long Body) and TF (Short Body) glow plugs is
based on the size of the hole that glow plug filament is located in.
The Long Body plugs have a slightly larger hole which results in a
slightly hotter glow plug element. However there is not a lot of
difference between a TC and TF glow plug and you can use them
interchangeably.